If you are enrolled in a plan since 2010, then no, your insurer can’t legally deny you coverage or charge you higher premiums because you have a pre-existing condition.
The Affordable Care Act, passed in 2010, made it illegal for insurers to deny you coverage or charge high rates for pre-existing conditions. Additionally, if your health changes and you develop a chronic medical condition while enrolled in a health plan, your insurance carrier cannot raise your rates because of that medical condition. However, annual premium increases may apply to your plan for other reasons.
If, however, you are enrolled in a plan that started before 2010, you have a “grandfathered plan.” These plans can cancel your coverage or can charge you higher rates due to a pre-existing condition.